Copying apparatus with automatic bottom feeder

Abstract

A bottom feeder for copy paper feeding has means for imparting a curvature to the sheets, the curvature being in the direction the sheets will be withdrawn. The curvature provides transverse rigidity to permit lifting weight of stack off the bottom sheet. This facilitates withdrawing the sheets one at a time from the bottom of the stack. A curved paper tray imparts a curvature to the paper. A pair of holding clamps are provided, one on either side of the stack of paper, which are partially withdrawn from the sides of the paper stack so that paper may be added to the stack. When sheets are to be fed, the clamps which comprise a pair of plates having a friction material on the paper facing side thereof are moved in to engage the sides of the stack of paper. An arrangement is provided to thereafter lower the paper tray slightly from the bottom of the stack, or lift the clamps and the curved paper stack. In either event, the pressure of the stack weight is now removed from the bottom sheet. A vacuum type feed belt which passes under the stack of paper can now pick off one sheet at a time without the sheets being restrained by friction against the paper tray or created between the tray and the stack of paper. The friction material on the holding plates in a preferred embodiment comprises bristles angled upward away from the paper tray to retain the stack lifted from the paper tray while allowing relatively easy withdrawal of each sheet. A stack-height sensor, preferably a switch on the face of one of the plates, senses the condition where, as the height of the stack diminishes, the pressure of the holding clamp plates may be slightly reduced to avoid binding of the paper. Timing means, which in the disclosed embodiment comprise cams riding on a common shaft, are provided to coordinate the movement of the clamps toward and away from the sides of the stack with the movement of the paper tray away from the bottom of the stack of paper.

What is claimed is: 
     
       1. In an electrophotographic apparatus designed to make successive copies utilizing a stack of copy paper utilizing a feeding arrangement configured to act on the stack in a way which successively moves pieces of paper off the bottom of the stack when the latter is placed in a feed tray, the paper feed assembly comprising means for imparting a curvature to the stack of paper,   a pair of holding clamps arranged on either side of the feed tray facing the feed tray to hold said stack of copy paper in its curved position, said holding claims comprising a pair of plates, one on each side of said paper stack, said plates being movable into and out of engagement with the sides of said paper stack to hold said stack of copy paper in its curved position.   means for causing relative movement between the copy paper stack and the feed tray to allow withdrawal of the bottom sheet of copy paper, and   means for withdrawing the bottom sheet of copy paper while the feed tray is at a distance from the paper stack.   
     
     
       2. An apparatus as claimed in claim 1 wherein said feed tray is curved, the radius of curvature being in the direction of paper feed, to impart a corresponding curvature to the stack of paper. 
     
     
       3. An apparatus as claimed in claim 2 further comprising timing means for timing paper withdrawal including holding a curved tray comprising the feed tray in a first position wherein said copy may be loaded in said stack, means for moving the tray away from the paper stack and moving the holding clamps against the curved paper stack so that a sheet or sheets of paper may be removed.   
     
     
       4. An apparatus as claimed in claim 1 wherein said means for withdrawing the bottom sheet comprises a vacuum belt passing the bottom of the paper stack and along the top of the feed tray. 
     
     
       5. An apparatus as claimed in claim 1 further comprising friction material on a paper confronting surface of each of said plates for engaging the edges of the stack of copy paper. 
     
     
       6. An apparatus as claimed in claim 5 further comprising means for imposing a curvature on the stack of paper, the radius of curvature being in the direction of withdrawal of the paper. 
     
     
       7. An apparatus as claimed in claim 6 wherein said means for imposing said curvature comprises a curved plate arranged to function as the feed tray. 
     
     
       8. An apparatus as claimed in claim 5 wherein said friction material comprises a bristle mat, the bristles being directed substantially toward the edges of the paper stack. 
     
     
       9. An apparatus as claimed in claim 8 wherein the friction material comprises bristles oriented at an angle of about 60° from the confronting plates, the bristles being angled up relative to the feed tray to support the paper. 
     
     
       10. An apparatus as claimed in claim 1 further comprising means cooperating with the holding plates for controlling the pressure of the holding clamps against the paper stack of the feed tray comprising means for monitoring the height of the stack and means responsive to the monitoring means for reducing the pressure of the holding clamps against the sides of the paper stack. 
     
     
       11. An apparatus as claimed in claim 10 wherein said holding clamps comprise a pair of plates facing the sides of said stack of paper, said pressure control means comprising a shaft extending between and coupled to said plates, said shaft incorporating a gear and screw for modifying the length of said shaft, and a motor responsive to said stack height sensor to rotate said gear and said screw modifying the length of said shaft and thereby the stack support distance between the plates. 
     
     
       12. An apparatus as claimed in claim 3 wherein said timing means further comprise a control shaft carrying first and second cams, said first cam being positioned and shaped to engage said feed tray and raise it to a paper feed stack loading position, a second cam being positioned to move said holding clamps to a position away from the paper stack, so that paper may be added to the stack. 
     
     
       13. In an electrophotographic apparatus designed to make successive copies utilizing a stack of copy paper by utilizing a feeding arrangement configured to act on the stack in a way which successively moves pieces of paper off the bottom of the stack when the latter is placed in a feed tray, said feed tray including means for creating curvature in the stack in the direction of paper withdrawal, the paper feed assembly comprising a pair of holding clamps arranged on either side of the feed tray facing the feed tray,   means for moving the holding clamps laterally relative to the paper stack on the feed tray,   means for moving the paper tray toward and away from the paper stack,   means for withdrawing the bottom sheet of copy paper while the feed tray is at a distance from the paper stack, and   timing means for coordinating the movement of said clamp moving means, said tray moving means and said paper withdrawing means.   
     
     
       14. An apparatus as claimed in claim 13 wherein the paper tray is curved, the radius of curvature being in the direction of paper feed, to impart a corresponding curvature to the stack of paper. 
     
     
       15. An apparatus as claimed in claim 14 wherein said holding clamps comprise a pair of plates, one on each side of said paper stack, movable into and out of engagement with the paper stack. 
     
     
       16. An apparatus as claimed in claim 15 further comprising friction material on a paper confronting surface of each of said plates for engaging the edges of the stack of copy paper. 
     
     
       17. An apparatus as claimed in claim 16 wherein the friction material comprises bristles oriented at an angle of about 60° from the confronting plates, the bristles being angled up relative to the feed tray to support the paper. 
     
     
       18. An apparatus as claimed in claim 17 wherein said timing means further comprise a control shaft carrying first and second cams, said first cam being positioned and shaped to engage said feed tray and raise it to a paper feed stack loading position, a second cam being positioned to move said holding clamps to a position away from the paper stack, so that paper may be added to the stack. 
     
     
       19. An apparatus as claimed in claim 18 further comprising means cooperating with the holding plates for controlling the pressure of the holding clamps against the paper stack of the feed tray comprising means for monitoring the height of the stack and means responsive to the monitoring means for reducing the pressure of the holding clamps against the sides of the paper stack. 
     
     
       20. An apparatus as claimed in claim 19 wherein said holding clamps comprise a pair of plates facing the sides of said stack of paper, said pressure control means comprising a shaft extending between and coupled to said plates, said shaft incorporating a gear and screw for modifying the length of said shaft, and a motor responsive to said stack height sensor to rotate said gear and said screw modifying the length of said shaft and thereby the stack support distance between the plates. 
     
     
       21. An apparatus as claimed in claim 16 wherein said timing means further comprise a control shaft carrying first and second cams, said first cam being positioned and shaped to engage said feed tray and raise it to a paper feed stack loading position, a second cam being positioned to move said holding clamps to a position away from the paper stack, so that paper may be added to the stack.